Steadiness in one-legged stance: development of a reliable force-platform testing procedure.

Postural steadiness in one-legged stance has potential for evaluation of unilateral injuries and disorders, but any test protocol must be demonstrated to be both feasible and reliable. A testing protocol for using a force platform to measure steadiness in one-legged stance with eyes opened and eyes closed was successfully developed, and its within-session retest reliability was investigated in a group of 24 young, healthy subjects. Strategies were used to minimize the loss of data for trials in which the subjects incurred significant loss of balance from the one-legged position. The performance scores examined were the standard deviation of the three orthogonal force components and the two horizontal center of pressure (CP) coordinates averaged over four consecutive five-second trials. The retest coefficients for all test conditions were substantially improved compared with testing protocols reported earlier. Retest reliability was higher for performance scores based on force measures than for performance scores based on CP measures. The difference was statistically significant in two of the stances, with a similar trend in the other two stances. Further, factor analysis showed that force measures were the best predictors of steadiness in one-legged stance. Analysis of variance failed to detect any systematic effect for leg preference or laterality on steadiness in one-legged stance with eyes opened or eyes closed in the healthy subjects with no history of injury (p greater than .05). The test protocol described enables the development of clinical or experimental trials with repeated-measures design using the subject's nonaffected leg as a control.